Zinc , Arsenic , and Boron on the Growth of Plants. 291 
reduced to 1/250,000,000 (Curve 10). The sodium arsenite appears to 
retain its toxicity for barley to a remarkable degree, so that very small 
quantities do not act as indifferent agents, but as consistent poisons. 
gm. 
Curve 9. Showing the mean values of the dry weights of nine series of barley plants (‘ English 
Archer’) grown in the presence ol sodium arsenite and nutrient salts. (March n-May 15, 1911.) 
gm. 
Curve 10. Showing the mean values of the dry weights of ten series of barley plants (‘ Archer ’) 
grown in the presence of sodium arsenite and nutrient salts. (Feb. 10-April 18, 1913.) 
Peas. The results obtained with peas grown in two different seasons 
are remarkably divergent in some respects. As with barley, 1/100,000 is 
the greatest strength of sodium arsenite in which the plants can grow at all, 
and as the solution is made more dilute the amount of growth increases 
steadily. With peas (‘ Sutton’s Harbinger ’) grown in the summer months 
